262 LEADING AMERICAN MEN OF SCIENCE 



von Buch's theory of craters of elevation and the establishment of 

 a true theory of the origin of volcanic cones. A volcanic cone is 

 not a sort of blister on the earth's crust, formed by the uplifting of 

 the strata by intumescent lavas beneath, but is simply a pile of 

 erupted material. 



In the years from 1871 to 1888, Dana was engaged in the inves- 

 tigation of the so-called "Taconic Question." A great series of 

 schists, quartzites, and crystalline limestones, extending from Can- 

 ada through western Vermont, Massachusetts, and Connecticut, 

 and southeastern New York, had been described by Ebenezer 

 Emmons, in 1842,* as the Taconic system, and by him and his 

 followers was claimed to be older than the Champlain group of 

 the New York geologists (now classified as Cambrian and 

 Ordovician). Dana devoted much time to the investigation of 

 the subject in the field. He also fortunately got hold of the 

 notes of Rev. Augustus Wing, and thus rescued from unde- 

 served oblivion the discoveries of a patient and conscientious 

 investigator who had been too modest to publish his work. The 

 result of the labors of Dana, Wing, Walcott, and others was the 

 conclusive proof that the so-called Taconic system is not pre- 

 Cambrian but metamorphosed Cambrian and Ordovician. 



The Taconic question was not merely, though it was primarily, 

 a question of local stratigraphy. The settlement of the age of the 

 Taconic rocks fixed the date of the first important epoch of oro- 

 genie disturbance in the post-Archaean history of North America. 

 The Taconic revolution stands as a time boundary between 

 Ordovician and Silurian time. The settlement of the Taconic 

 question was important, also, as establishing a perfectly clear 

 case of somewhat highly crystalline rocks of Paleozoic age. It 

 was thus a refutation of the belief of a school of geologists now 

 extinct or nearly so, that all the crystalline schists and associated 

 rocks are Archaean, and that a crystal is as good as a fossil to 

 determine the age of a rock. 



When the first edition of the Manual of Geology was published, 

 opinions were still divided in regard to the origin of the hetero- 

 1 Geology of New York, Part 2, pp. 135-164. 



